This invention relates to water base drilling fluids. More particularly, the invention relates to water base drilling fluids having improved characteristics which allow low temperature drilling operations, inhibit formation of gas hydrates which form at low temperatures and high pressures, reduce shale dispersion which results in improved wellbore stability, reduce fluid loss, and are environmentally more safe.
Oil-in-water emulsion drilling fluids (or muds) generally comprise water, oil, emulsifier, clays or polymers, and various treating agents which control the physical, chemical and/or rheological properties of drilling fluids in wellbores. Any type of aqueous drilling fluid can be converted to an emulsion drilling fluid through the simple expedient of adding the desired amount of oil and emulsifier. The drilling fluid serves to remove chips, cuttings and the like produced by a rotating drill bit from a wellbore by circulating the drilling fluid down from the surface of the well, through the drill string, and out through openings in the drill bit such that the drilling fluid is then circulated upwardly in the annulus between the side of the wellbore and the rotating drill string.
The selection of a drilling fluid is primarily dependent upon the geological formation being drilled and the problems associated with such formation. Principal concerns in selection of a drilling fluid are temperature drilling conditions, formation of gas hydrates, shale dispersion, and drilling fluid loss and environmental requirements. Classically, temperature concerns associated with drilling oil/gas wells have been associated with deep hot wells (&gt;300.degree. F.); however, for deep water and/or Artic drilling low temperatures are a concern for two principal reasons: (1) freezing of the mud due to low temperature, especially if the well must be shut in for long durations and (2) the formation of gas hydrates under low temperature and high pressure conditions after the influx of gas. The present invention provides a drilling fluid additive which overcomes these and other problems in the art as more particularly disclosed hereinafter.